Specify API version for Bukkit to stop legacy material loading (Closes #595)

bootstrap/bukkit/src/main/resources/plugin.yml

@@ -4,6 +4,7 @@ author: ${project.organization.name}
 website: ${project.organization.url}
 version: ${project.version}
 softdepend: ["ViaVersion"]
+api-version: 1.13
 commands:
   geyser:
     description: The main command for Geyser.